Satellite communications systems transmit content over large geographic regions. In a typical satellite communications system, end users interface with the system through user terminals. The user terminals communicate, via one or more satellites, with one or more gateway terminals. The gateway terminals may process and route data to and from one or more networks according to various protocols.
A typical hub-spoke spot beam satellite communications system may include a non-processing “bent pipe” spot beam satellite, many user terminals, and a smaller number of gateway terminals. Each user terminal may be connected to a network, such as the internet, via a series of communication links.
A forward link of a satellite communications system may consist of forward uplink transmissions from a gateway terminal to a satellite, a “bent pipe” repeater at the satellite, and forward downlink transmissions to a group of user terminals located in a common spot beam. The forward link may carry data from a gateway terminal to many different user terminals. The forward link may utilize, for example, time Division Multiplexing (TDM) and/or Frequency Division Multiplexing (FDM) of data into RF transmissions.
A return link of a satellite communications system may consist of return uplink transmissions from user terminals in a common spot beam to a satellite, and return downlink transmissions from the satellite to a gateway terminal servicing the spot beam. Transmissions from many user terminals may utilize the return link using Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Code Division Multiple Access (CDMA), or the like.
In a typical satellite communications system, imperfections or differences between oscillators at the gateway, the satellite, and the user terminals can lead to frequency and timing errors. These errors may cause differences between actual and expected frequencies and symbol rates. As a result of the frequency errors, burst acquisition in a conventional satellite communications system may include a search over frequency. A substantial portion of signal processing design may be driven by frequency uncertainty, and a substantial portion of the processing resources may be used to accommodate the frequency uncertainty and estimate the frequency error. These errors also increase overhead, since ambles may need to be significantly longer to allow effective frequency estimation.
Reducing the frequency and timing errors can simplify system design and minimize overhead. Reducing the frequency error may eliminate the need for a frequency search prior to decoding transmitted data. This can improve efficiency by reducing system hardware requirements and increasing the number of bursts per second that can be processed.
Thus, there is a need in the art for methods and systems that reduce frequency and timing errors in satellite communications systems.